Occasionaly you’ll get email spam for “vintage erotica” usually consisting of these short black and white loops of (assumedly) burlesque performers strutting around topless. It made me curious whether anyone actually owns the rights to this old stuff at this point, or does the “rights” to this sort of 40’s and 50’s stuff expire after awhile?
You can just bet that any clips of Bettie Page are owned, & carefully managed.
I’ve seen a few “stag films” at The Prelinger Archives. I’ve noticed the women in those films were, uh, full figured.
That’s also a great site for those 50s educational films, not to mention a ton of free downloadable music (including The Grateful Dead).
Wow, a lot of those 50’s stag films were quite tame. I’m not complaining, actually they were very tasteful. I’m just chuckling at the concept of a bunch of guys crowded around an 8mm projector hooting and hollering at a film of a woman *almost * taking her top off 
The rights issues for these works are a bit complicated. You need to know when they were made, whether or not they were properly copyrighted in the first place, and whether or not they were renewed in a timely fashion. This copyright status chart lists the consequences of the various permutations.
Any film that was never copyrighted in the first place is in the public domain. How do you know if this was the case? Prior to 1989, a copyright notice had to be placed on the work itself. But that means you have to get hold of a guaranteed original copy. While it was possible to lose copyright if you neglected to continue listing the notice, you wouldn’t if somebody pirated the film - which happened often with erotica. Even the Library of Congress doesn’t always have good records of original or renewed registrations.
If the copyright was placed and was renewed then there is a rights owner. Nobody keeps a central registry of them or their current locations, so finding rights is usually the hardest part of any attempt to bring back vintage short films of any kind.
Of course, the pirates of any era, today included, didn’t care about rights.